Method and apparatus for electromagnetic confinement of molten metal in horizontal casting systems

ABSTRACT

The present invention provides an apparatus for strip casting of molten metal including a pair of casting rollers adapted to receive molten metal along a horizontal axis, wherein a vertical distance separating the pair of casting rollers defines a molding zone; and an electromagnetic edge containment apparatus positioned on each side of the molding zone having an induction coil wound about a portion of a magnetic member to generate magnetic lines of force upon application of a current, wherein the poles of the magnetic member are positioned distal from to aligned to the planar sidewall of the casting rollers and the current provides magnetic lines of force perpendicular to said horizontal axis that contain the molten metal in contact to the casting rollers without substantially increasing the temperature of the molten metal.

FIELD OF THE INVENTION

The present invention relates to the continuous casting of metal strip,and more particularly, to the electromagnetic confinement of moltenmetal in a continuous casting system.

BACKGROUND OF THE INVENTION

Continuous casting of metals is performed in twin-roll casters and beltcasters or combinations thereof. Methods are available for casting bothin the horizontal and in the vertical direction. In particular, thesteel industry has recently developed high speed twin roll strip casterswhich operate in the vertically down direction.

Up to the present, the mechanical edge dams have been employed toprovide containment of the molten metal in the casting zone. Suchdevices have included the caterpillar type edge dams that move with thestrip (as in the Hazelett casters) or fixed edge dams that are pressedagainst the surface of the rolls. The latter is used in the twin-rollsteel strip casting industry. Such fixed mechanical edge dams have ashort service life as they get eroded by contact with the cold sidewallof the rolls. In addition, such mechanical edge dams provide sites forthe formation of skulls that have a tendency to be sheared off and thusenter the cast strip to render the microstructure metallurgicallyundesirable. Caterpillar edge dams, while well proven for the thickerslab castings (10-25 mm thick), become impractical for thin stripcasters or twin drum casters of the steel industry where the crosssection to be contained changes sharply along the casting zone.

Electromagnetic edge dams have been employed in the prior art in thestrip casting of metals in vertical twin drum (roller) casting systems.Electromagnetic edge dams of a magnetic system type use a combination ofa magnet assembly and an AC coil to generate confinement forces.Electromagnetic edge dams of an induction system type rely solely on anAC coil to generate the containment forces.

The magnetic system electromagnetic edge dams use a magnetic memberwhich comprises a yoke or core connecting two pole faces disposed oneither side of the gap on which the molten metal is to be confined. Themagnetic member is made of a ferromagnetic material and is surroundedover a given length of the yoke by a coil carrying an AC current. Themagnetic flux generated by the flow of the current into the coil istransmitted to the poles of the magnet through the yoke and establishescontainment forces at the metal surface in the gap.

Typically, in magnetic systems, part of the magnetic member is coveredwith an electrically conductive shield to minimize leakage of flux in adirection away from the gap. Such magnetic confinement systems have theadvantage that the confinement current need not be as high as comparedto those systems using solely an induction coil. If a stronger magneticfield is required, it can be achieved with the same current level byreducing the area of the pole faces to concentrate the field. However,such systems are not without disadvantages. For example, such systemstypically have poor operating efficiency resulting from core losses andlosses due to magnetic hysterisis when an alternating magnetic field isapplied to the magnetic material. Additionally, high temperatures aretypically generated that need to be dissipated by cooling in order toprevent damage to the magnetic system.

Induction confinement systems typically employ a shaped inductorpositioned close to the gap in which the molten metal is to becontained. The AC current flowing in the inductor generates inducedcurrents as well as a time-varying magnetic field on the surface of themolten metal to be contained. The interaction between the current andthe magnetic field provide containment forces. To improve efficiency, amagnetic member is built around the inductor to focus the current to theinductor surface facing the molten metal. Induction coil systems aregenerally simpler in design than magnetic systems. However, inductionsystems are disadvantageously limited in terms of the maximummetallostatic head that can be contained by the system. The maximummetallostatic head that can be supported in induction coil systems islimited, because induction coil systems require very high inductorcurrents to provide adequate containment forces, wherein such highcurrents are accompanied by increased heat generation, which in turnhinders or slows the solidification process during casting.

Referring to FIG. 1, in vertical twin roll casters, the molten metalhead against which containment must be provided tends to be very high.For typical operating condition, the metal head height H₁ is about 65%the radius of the casting rolls. Therefore, electromagnetic edge damapparatus used in vertical twin roll casters must provide a magneticfield strong enough to contain a metal pool having a head height H₁ thatis 65% the radius of the casting rolls. Such electromagnetic edge damshave not been successfully commercialized for two reasons. First, thehigh current required to contain the molten metal pool creates standingwaves on the top surface of the metal pool that are too large inmagnitude for the casting process. Second, the large electromagneticforces needed to contain the molten metal head formed atop verticalroller caster systems create induction heating on the metal pool'ssidewall, which interferes with the solidification process.

U.S. Pat. No. 4,936,374 describes a vertical casting system andelectromagnetic confinement apparatus having the disadvantages describedabove. Further, U.S. Pat. No. 4,936,374 describes casting rollers havinga rim portion, in which the containment magnetic field is conductedthrough the rim portion of the casting roll. In addition to inductionheating and wave generation, the rim portions of the casting rollsdisclosed in U.S. Pat. No. 4,936,374 produce a ridge in the cast productand therefore fail to provide a casting strip having uniform sidewalls(edges). The ridge formed in the casting strip produced using theapparatus and method disclosed in U.S. Pat. No. 4,936,374 must bemachined prior to rolling of the casting strip. Additional machiningdisadvantageously adds to the cost of the production.

Accordingly, a need remains for a method of high-speed continuouscasting of metals and alloys, which achieves uniformity in the caststrip surface, provides good molten metal containment in the castingzone, and results in strip edges which can be rolled without needing tobe machined by trimming.

SUMMARY OF THE INVENTION

The present invention overcomes the above-described obstacles anddisadvantages by providing an electromagnetic confinement apparatusincorporated into a horizontal casting apparatus, wherein thepositioning of the electromagnetic confinement apparatus and a magneticfield that is produced by an alternating current provides a cast metalstrip having substantially uniform edges (sidewalls). The presentinvention further provides a method and apparatus for producing a castmetal strip, which provides a means for adjusting the profile of thecast metal strip's sidewall.

In one embodiment of the present invention, the current applied throughthe electromagnetic confinement apparatus, as well as, the positioningof the electromagnetic confinement apparatus to the molding zone of thehorizontal casting apparatus is selected to provide a cast metal striphaving substantially uniform edges, in which the sidewall of the castmetal strip edges may be substantially flat, or concave or convex inrelation to the cast metal strip's centerline. The cast metal strip'ssubstantially uniform edges allows for the cast metal strip to be rolledwithout further machining. Broadly, one embodiment of an apparatus ofthe present invention comprises:

-   -   (a) a pair of casting rollers adapted to receive molten metal        along a horizontal axis, wherein a vertical distance separating        the pair of casting rollers defines a molding zone;    -   (b) an electromagnetic edge containment apparatus positioned on        each side of the molding zone, comprising an induction coil        wound about a portion of a magnetic member to generate magnetic        lines of force upon application of a current, wherein said        magnetic member comprises a first and second pole positioned        distal from and aligned to a sidewall of said pair of casting        rollers and the current provides magnetic lines of force        perpendicular to said horizontal axis that contain the molten        metal in contact to the casting rollers with substantially no        increase in temperature to the molten metal; and    -   (c) a means for supplying the molten metal to the molding zone        along said horizontal axis from a tundish while ensuring said        molten metal remains substantially non-oxidized, wherein the        tundish is separated from the molding zone by a distance to        substantially eliminate wave generation within the tundish by        the magnetic lines of force.

In another embodiment of the apparatus of the present invention, ahorizontal roller casting apparatus is provided in which containment ofthe metal through the apparatus is provided by the combination of amechanical edge dam and an electromagnetic edge dam. Broadly, theinventive casting apparatus comprises:

-   -   (a) a pair of casting rollers adapted to receive molten metal        along a horizontal axis, wherein a vertical distance separating        the pair of casting rollers defines a molding zone;    -   (b) a tip delivery structure positioned to supply the molten        metal to the molding zone along said horizontal axis from a        tundish while ensuring said molten metal remains substantially        non-oxidized; and    -   (c) an edge containment apparatus positioned on each side of the        molding zone, said edge containment apparatus comprising:        -   a mechanical edge dam positioned overlying at least an end            portion of said tip delivery structure and partially            extending towards said molding zone, and        -   an electromagnetic edge dam comprises a first and second            magnetic pole positioned distal from and aligned to a            sidewall of said pair of casting rollers and overlying a            portion of said mechanical edge dam partially extending            towards said molding zone, wherein said electromagnetic edge            dam provides magnetic lines of force perpendicular to said            horizontal axis that contain the molten metal in contact to            the casting rollers.

In each embodiment, the vertical distance separating the horizontallydisposed pair of casting rollers provides a metal head height thatallows for containment of the molten metal by magnetic lines of forcethat are provided by an electromagnetic containment device without asubstantial increase in the temperature of the molten metal. For thepurposes of this disclosure, the term “positioned distal from andaligned to a sidewall of said pair of casting rollers” is intended todenote that the poles of the electromagnetic edge dam do not extendtowards the casting apparatuses centerline beyond a plane defined by thesidewall of the casting rollers, but are positioned within close enoughproximity to the castings roller's sidewall to provide a sufficientmagnetic field to contain molten metal within the molding zone. It isnoted that the poles of the electromagnetic edge dam may be adjustedfrom adjacent to the casting rollers sidewall to any distance from thesidewall, so long as sufficient containment forces are provided by thepoles to the molding zone. In one embodiment, the sidewall of thecasting roller may be substantially planar. The term “substantiallyplanar” with respect to the casting roller's sidewall denotes that thecasting roller does not incorporate a lip portion. In one embodiment,the electromagnetic lines of force are produced by an alternatingcurrent having a frequency ranging from 40 Hz to 10,000 Hz through theelectromagnetic edge containment device.

In another embodiment of the present invention, a belt casting system isprovided that employs electromagnetic edge containment and produces ametal strip having substantially uniform edges, wherein thesubstantially uniform edges allows for the cast metal strip to be rolledwithout further machining. Broadly, the inventive belt casting systemfor strip casting of molten metal comprising:

-   -   (a) a pair of opposing endless metal belts, each of the pair of        opposing endless metal belts passing over a roller and having a        periphery substantially aligned to a periphery of the roller,        said each of said opposing endless metal belts having a surface        for accepting molten metal, wherein a vertical dimension        separating the pair of opposing endless metal belts defines a        molding zone;    -   (b) an electromagnetic edge containment apparatus positioned on        each side of the molding zone comprising an induction coil wound        about a portion of a magnetic member to generate magnetic lines        of force upon application of a current, wherein the current        provides magnetic lines of force that contain the molten metal        within a width and in contact to at least a portion of said pair        of opposing endless metal belts with substantially no increase        in temperature to the molten metal; and    -   (c) a means for supplying said molten metal to the molding zone        along a horizontal axis from a tundish, the tundish separated        from said molding zone by a distance to substantially eliminate        wave generation within the tundish by the magnetic lines of        force.

In another aspect of the present invention, a casting strip is providedthat may be formed by the above casting apparatus. Broadly, the caststrip comprises:

-   -   (a) a first shell;    -   (b) a second shell; and    -   (c) a central portion between said first shell and said second        shell, said central portion comprising grains having an equiaxed        structure, wherein said cast metal strip has sidewall edges        being substantially uniform.

In another aspect of the present invention, a method is provided forcasting a metal strip in which a magnetic field is utilized to controlthe geometry of the metal strip's sidewall. Broadly, the inventivemethod comprises:

-   -   providing molten metal to a molding zone along a horizontal        axis;    -   containing said molten metal within said molding zone with a        magnetic containment means; and    -   casting said molten metal into a cast metal strip, wherein        sidewall geometry of said cast metal strip is configured by        adjusting said magnetic containment means.

The magnetic field may be adjusted to provide a metal casting stripsidewall geometry that is flat or is concave or convex relative to thecenterline of the cast metal strip. In one embodiment, the magneticcontainment means may include an induction coil wound about a magneticmember to generate magnetic lines of force upon application of acurrent. The magnetic member having a first and second magnetic polepositioned distal from to adjacent to the molding zone.

The magnetic lines of force produced by the magnetic containment meansmay be adjusted by increasing or decreasing the current through theinduction coil or by changing the positioning of the magneticcontainment means relative to the molding zone. Positioning the firstand second magnetic poles of the magnetic containment means adjacentto-the molding zone may produce a cast metal strip having a concavesidewall and positioning the first and second magnetic poles of themagnetic containment means distal from the molding zone may produce acast metal strip having a convex sidewall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (side cross sectional view) is a schematic of a portion of avertical roller caster casting apparatus depicting a molten metal headand a pair of rolls operated according to the prior art.

FIG. 2 a (side cross sectional view) is a schematic of one embodiment ofa horizontal casting apparatus having electromagnetic edge dams inaccordance with the present invention.

FIG. 2 b (side cross sectional view) depicts one embodiment of a twinbelt caster equipped with an electromagnetic edge dam apparatus inaccordance with the present invention.

FIG. 3 (side cross sectional view) depicts the molding zone of theinventive horizontal casting device.

FIG. 4 depicts a table summarizing the magnetic field density that isrequired to contain a molten pool of aluminum at different head heights.

FIG. 5 depicts a plot of the magnetic field strength produced by anelectromagnetic containment device in accordance with the presentinvention at varying currents and distances wherein the distance ismeasured from the sidewall of the caster roll.

FIG. 6 (side cross sectional views) depicts a sectional view taken alongthe lines 2-2 in FIG. 2 a, and illustrate the positioning of theelectromagnetic edge dams in relationship to the sidewall of the rollercasters.

FIGS. 7 a-7 d provide a sectional view of the electromagnetic edge damapparatus of the present invention illustrating the path of the magneticlines of force in relation to the roller casters of the horizontalroller caster casting apparatus.

FIGS. 8 a-c (side view) illustrate different pole face angles andorientations in accordance with the present invention.

FIG. 9 illustrates an exemplary embodiment of the present inventionwherein a magnetic member has a split core design.

FIG. 10 illustrates an exemplary embodiment of the present inventionwherein the magnetic member has a laminate design.

FIG. 11 illustrates an exemplary embodiment of the present inventionwherein a mechanical edge dam is used in conjunction with anelectromagnetic edge dam.

FIG. 12 depicts a table summarizing the push of the electromagnetic edgedam.

FIGS. 13 a-c are pictorial representations of sidewall of a castingstrip.

FIGS. 14 a-b are photographic representations of the edges of the stripmade with a high magnetic force in the electromagnetic dam.

FIG. 15 is a pictorial representation of a casting strip having a flatedge profile (straight edge).

FIG. 16 is a pictorial representation of a casting strip following an87% reduction (acceptable degree of edge cracking).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides an electromagnetic edge dam that confinesmolten metal to the molding zone of a horizontally disposed rollercasting or belt casting system with a magnetic field that is produced bya lower AC current than was previously possible. By providing sufficientelectromagnetic containment means at lower AC currents, the presentinvention utilizes electromagnetic confinement without creating asubstantial increase in the temperature of the molten metal or producingwave generation effects.

As discussed above, in prior vertical casting methods with larger moltenmetal head height, larger magnetic forces are required in order tocontain the greater pressure produced by the molten metal, whereinlarger magnetic forces typically require higher currents that generateheat. For example, to contain molten aluminum against a 300 mm height,as representative of typical vertical casting methods, a minimummagnetic field intensity of 0.24 T would be needed. In the presentinvention, the metal head height is kept low, as achieved by ahorizontally disposed casting system, so that the required containmentcan be met with relatively low magnetic field density. For example, a 50mm head height in a horizontal casting apparatus consistent with thepresent invention requires a magnetic field density of only 0.055 T tocontain molten aluminum in the horizontal position while casting. Thepresent invention is now discussed in more detail referring to thedrawings that accompany the present application. In the accompanyingdrawings, like and/or corresponding elements are referred to by likereference numbers.

Referring to FIG. 2 a, in one embodiment of the present invention, ahorizontal roller casting apparatus 10 is provided having anelectromagnetic edge dam 15 positioned to provide magnetic lines offorce to confine molten metal M within the molding zone 20 of theapparatus 10, wherein the magnetic lines of force extend along a planeperpendicular to the plane on which the casting is drawn. The horizontalroller casting apparatus 10 is practiced using a pair ofcounter-rotating cooled rolls R₁ and R₂ rotating in the directions ofthe arrows A₁ and A₂, respectively. By the term horizontal, it is meantto denote that the cast strip is produced along a horizontal plane, inwhich the horizontal plane is parallel to section line 2-2, or at anangle of plus or minus about 30° from the horizontal plane.

Referring to FIG. 2 b, in one embodiment of the present invention, ahorizontal belt casting apparatus 10′ is provided having anelectromagnetic edge dam 15 positioned to provide ma genetic lines offorce to confine molten metal M within the molding zone 20 of theapparatus 10, wherein the magnetic lines of force extend along a planeperpendicular to the plane 2-2 on which the casting is drawn. Thehorizontal belt casting apparatus 10′ is practiced using a pair ofcounter-rotating belts B₁ and B₂ rotating in the directions of thearrows A₁ and A₂, respectively. It is noted that although the followingfigures are directed towards the horizontal roller caster 10 depicted inFIG. 2 a, the following description is equally applicable to thehorizontal belt caster 10′ disclosed in FIG. 2 b with the exception thatinstead of the molten metal contacting the roller casters R₁, R₂ themolten metal is contacting the counter-rotating belts B₁, B₂. It isfurther noted, that further differences between the horizontal rollercasting apparatus 10 and the belt casting apparatus 10′ in accordancewith the present invention are noted when relevant throughout thefollowing portions of the specification.

Referring to FIG. 3, molten metal M is transported to the molding zone20 by a feed tip T, which may be made from a suitable ceramic material.The feed tip T distributes molten metal M in the direction of arrow Bdirectly onto the casting rolls R₁ and R₂ rotating in the direction ofthe arrows A₁ and A₂, respectively. Gaps G₁ and G₂ between the feed tipT and the respective rolls R₁ and R₂ are maintained as small as possibleto prevent molten metal from leaking out and to minimize the exposure ofthe molten metal to the atmosphere. A suitable dimension of the gaps G₁and G₂ is about 0.01 inch (0.25 mm). A plane L through the centerline ofthe rolls R₁ and R₂ passes through a region of minimum clearance betweenthe rolls R₁ and R₂ referred to as the roll nip N.

The molten metal M delivered from the feeding tip T directly contactsthe cooled rolls R₁ and R₂ at regions 18 and 19, respectively. Uponcontact with the rolls R₁ and R₂, the metal M begins to cool andsolidify. The cooling metal produces an upper shell 16 of solidifiedmetal adjacent the roll R₁ and a lower shell 17 of solidified metaladjacent to the roll R₂. The thickness of the shells 16 and 17 increasesas the metal M advances towards the nip N. Large dendrites 21 ofsolidified metal (not shown to scale) are produced at the interfacesbetween each of the upper and lower shells 16 and 17 and the moltenmetal M. The large dendrites 21 are broken and dragged into a centerportion 12 of the slower moving flow of the molten metal M and arecarried in the direction of arrows C₁ and C₂.

The dragging action of the flow can cause the large dendrites 21 to bebroken further into smaller dendrites 22 (not shown to scale). In thecentral portion 12 upstream of the nip N, the metal M is semi-solidincluding a solid component including solidified small dendrites 22 anda molten metal component. The metal M in the region 23 has a mushyconsistency due in part to the dispersion of the small dendrites 22therein. At the location of the nip N, some of the molten metal issqueezed backwards in a direction opposite to the arrows C₁ and C₂. Theforward rotation of the rolls R₁ and R₂ at the nip N advancessubstantially only the solid portion of the metal (the upper and lowershells 16 and 17 and the small dendrites 22 in the central portion 12)while forcing molten metal in the central portion 12 upstream from thenip N such that the metal is completely solid as it leaves the point ofthe nip N.

Downstream of the nip N, the central portion 13 is a solid central layer13 containing the small dendrites 22 sandwiched between the upper shell16 and the lower shell 17. In the central layer 13, the small dendrites22 may be about 20 to about 50 microns in size and have a generallyequaixed (globular) shape, as opposed to having a columnar shape. Thethree layers of the upper and lower shells 16 and 17 and the solidifiedcentral layer 13 constitute a solid cast strip.

The rolls R₁ and R₂ serve as heat sinks for the heat of the molten metalM. In the present invention, heat is transferred from the molten metal Mto the rolls R₁ and R₂ in a uniform manner to ensure uniformity in thesurface of the cast strip. Surfaces D₁ and D₂ of the respective rolls R₁and R₂ may be made from a material of good thermal conductivity such assteel or copper or other metallic materials and are textured and includesurface irregularities (not shown) which contact the molten metal M. Thesurface irregularities may serve to increase the heat transfer from thesurfaces D₁ and D₂. The rolls R₁ and R₂ may be coated with a material toenhance separation of the cast strip from the rolls R₁ and R₂ such aschromium or nickel. In a preferred embodiment, the rolls R₁ and R₂,including surfaces D₁ and D₂, comprise a ferromagnetic material. In theembodiments of the present invention, in which the rolls R₁ and R₂ donot comprise a ferromagnetic material, the casting surfaces D₁, D₂ ofthe roller as well as the roller's sidewall may be coated with aferromagnetic materials.

The control, maintenance and selection of the appropriate speed of therolls R₁ and R₂ may impact the operability of the present invention. Theroll speed determines the speed that the molten metal M advances towardsthe nip N. If the speed is too slow, the large dendrites 21 will notexperience sufficient forces to become entrained in the central portion12 and break into the small dendrites 22. Accordingly, the presentinvention is suited for operation at high speeds such as about 25 toabout 400 feet per minute or about 100 to about 400 feet per minute orabout 150 to about 300 feet per minute. The linear speed that moltenaluminum is delivered to the rolls R₁ and R₂ may be less than the speedof the rolls R₁ and R₂ or about one quarter of the roll speed.High-speed continuous casting according to the present invention may beachievable in part because the textured surfaces D₁ and D₂ ensureuniform heat transfer from the molten metal M.

The roll separating force may be a parameter in practicing the presentinvention. The roll separating force is the force present between therolls due to the presence of the strip within the roll gap. The rollforce is particularly high when the strip is being plastically deformedby the rolls during roll casting. A significant benefit of the presentinvention is that solid strip is not produced until the metal reachesthe nip N. The thickness is determined by the dimension of the nip Nbetween the rolls R₁ and R₂. The roll separating force may besufficiently great to squeeze molten metal upstream and away from thenip N. Excessive molten metal passing through the nip N may cause thelayers of the upper and lower shells 16 and 17 and the solid centralportion 13 to fall away from each other and become misaligned.Insufficient molten metal reaching the nip N causes the strip to formprematurely as occurs in conventional roll casting processes. Aprematurely formed strip 20 may be deformed by the rolls R₁ and R₂ andexperience centerline segregation. Suitable roll separating forces areabout 25 to about 300 pounds per inch of width cast or about 100 poundsper inch of width cast. In general, slower casting speeds may be neededwhen casting thicker gauge aluminum alloy in order to remove the heatfrom the thick alloy. Unlike conventional roll casting, such slowercasting speeds do not result in excessive roll separating forces in thepresent invention because fully solid aluminum strip is not producedupstream of the nip.

In prior applications, roll separating force has been a limiting factorin producing low gauge aluminum alloy strip product but the presentinvention is not so limited because the roll separating forces areorders of magnitude less than in conventional processes. Aluminum alloystrip may be produced at thicknesses of about 0.1 inch or less atcasting speeds of 25 to about 400 feet per minute. Thicker gaugealuminum alloy strip may also be produced using the method of thepresent invention, for example at a thickness of about ¼ inch.

The aluminum alloy strip 20 continuously cast according to the presentinvention includes a first layer of an aluminum alloy and a second layerof the aluminum alloy (corresponding to the shells 16 and 17) with anintermediate layer (the solidified central layer 13) therebetween. Thegrains in the aluminum alloy strip of the present invention aresubstantially undeformed because the force applied by the rolls is low(300 pounds per inch of width or less). The strip is not solid until itreaches the nip N; hence it is not hot rolled in the manner ofconventional twin roll casting and does not receive typicalthermo-mechanical treatment. In the absence of conventional hot rollingin the caster, the grains in the strip 20 are substantially undeformedand retain their initial structure achieved upon solidification, i.e. anequiaxed structure, such as globular.

Continuous casting of aluminum alloys according to the present inventionis achieved by initially selecting the desired dimension of the nip Ncorresponding to the desired gauge of the strip S. The speed of therolls R₁ and R₂ may be increased to a desired production rate, or to aspeed that is less than the speed at which the roll separating forceincreases to a level that indicates that plastic deformation of thecasting strip is occurring between the rolls R₁ and R₂. Casting at therates contemplated by the present invention (i.e. about 25 to about 400feet per minute) solidifies the aluminum alloy strip about 1000 timesfaster than aluminum alloy cast as an ingot cast and improves theproperties of the strip over aluminum alloys cast as an ingot.

The molten metal M being delivered from the feed tip T is confinedwithin the molding zone 20 by at least an electromagnetic edge dam 15that is positioned to direct magnetic lines of force perpendicular tothe plane 2-2 on which the casting is being drawn. In one embodiment, anelectromagnetic edge dam 15 is positioned on each side of the castingapparatus. In a preferred embodiment, the molten metal M is confinedwithin the molding zone 20 during casting by a mechanical edge dam 55 incombination with an electromagnetic edge dam 15, wherein the mechanicaledge dam 55 is positioned proximate to the feed tip T and theelectromagnetic edge dam 15 is positioned overlying the terminating endof the mechanical edge dam 55 and provides confinement forces along theentire length of the molding zone 20, as depicted in FIGS. 6 and 11.

The current and/or frequency utilized by the electromagnetic edge dam 15to maintain the molten metal M within the molding zone 20 issubstantially less than typically required in prior casting apparatusesusing electromagnetic edge dams. In prior casting apparatus employingelectromagnetic edge dams, high magnetic force fields where required tocontain the molten metal, which resulted in induction heating within themolten metal that disadvantageously effected the solidification process.In the present invention, by reducing the magnitude of the requiredelectromagnetic force, the current and/or frequency conducted throughthe electromagnetic edge dam is also reduced, which in turnadvantageously reduces the incidence of induction heating on thesidewall of the molten metal in the molding zone.

Without wishing to be bound, but in the interest of further describingthe present invention, applicants' believe that the reduction in theelectromagnetic force that is required to contain the metal within themolding zone is related to the decreased head height H₂ of the moltenmetal from the feed tip T, as depicted in FIG. 3, as opposed to thegreater height H₁ of the molten metal pool disposed atop the rollercaster in prior vertical casting apparatuses, as depicted in FIG. 1. Asdiscussed above, the height H1 (or depth) of the molten pool atop thevertically disposed casting rollers is approximately 65% the height ofthe casting roller R₁, R₂ and can range from 8 inches to 20 inches, asdepicted in FIG. 1. Referring to FIG. 3, in the present invention, theheight H₂ of the molten metal as delivered from the tip feed T to themolding zone 20 can be on the order of about 1 inch, and in someexamples may be further reduced to 0.5 inches. Hereafter, the differencein vertical location of the metal level in the tundish and that of thecenter of the strip being cast is referred to as a “molten metal head”.

The relationship between the height of the molten metal head H₂ and themagnetic field density required for containing molten aluminum atdifferent head levels is best described through the following equations.First, the pressure exterted by the molten metal head, which themagnetic field must contain within the molding zone 20 is calculatedfrom:p=ρgH ₂

-   -   where p is is the magnetic pressure in Pa, ρ is the density of        the metal, g is the acceleration of gravity and H₂ is the height        of the molten metal head. The pressure produced by the molten        metal head in turn determines the strength of the magnetic field        that must be produced by electromagnetic edge containment device        15 to contain the molten metal head within the molding zone 20.        In the present invention, the height of the molten metal head H₂        that is being horizontally delivered to the molding zone 20 by        the feed tip T may be as low as 0.5 inches. The pressure that is        produced by the molten metal head of varying height H₂, from the        feed tip T of the present horizontal roller casting apparatus        10, was determined using the above equation and is listed in the        Table depicted in FIG. 4. To summarize the pressure ranged from        about 125 Pa for a metal head height H₂ of approximately 0.5        inches (12.7 mm) to about 2,492 Pa for a metal head height H₂ of        approximately 10 inches (254 mm).

The pressure required to contain the molten metal head H₂ within themolding zone 20 is then used in the following equation to determine therequired magnetic field density (B):p=B ²/2μ_(o)

-   -   where p is the magnetic pressure in Pa (Pascals), B is the        magnetic field density in T (Tesla) and μ_(o) is the        permeability of air (=4π×10 ⁻⁷ H/m). Referring to FIG. 4, from        the above equation, it is calculated that for a relatively high        molten metal head height H₂ for feed tip T delivery of        approximately 254 mm (10 inch), the magnetic field density        needed is 0.079 T (790 Gauss) and a molten metal head height H₂        of approximately 12.7 mm (0.5 inch), the magnetic field density        needed is approximately 0.0177 T. As illustrated in FIG. 4,        reducing the molten metal head height H₂ decreases the magnetic        field density that is needed to contain the molten metal M        within the molding zone 20. The magnetic field density required        to contain metal head heights consistent with the present        invention can be obtained with electromagnets at relatively low        current levels. In one embodiment, the electromagnetic edge dam        operates at approximately 2000 ampere turns (i.e. a coil of 10        turns drawing 200 A).

In another aspect of the present invention, the physical positioning ofthe electromagnetic edge dam, the molten metal head height and thestrength of the magnetic field can be varied to control the positioningof the edge of the molten metal within the molding zone with respect tothe roller casters R₁, R₂ sidewall. The strength of the magnetic fieldat different distances from the face (edge) of the roller casters may becalculated by the following equation:B_(L)=(μ_(o) nI/1)/{(2D/H)sin h(L/1)+(w/1)cos h(L/1)}

-   -   where:    -   B_(L)=magnetic field intensity at a distance L (m) in the gap        from the roll face.    -   nI=coil turns and current.    -   w=roll gap 1=√(μ_(r) δw/2) in which μ_(r)=relative permeability        of steel caster roll (taken as 600), δ=skin depth for steel        (material of the caster roll), and w is the roll gap.    -   D=distance between electromagnet pole and the roll face.    -   H=height of magnet pole.

Referring to FIG. 5, using the above equation, the magnetic fieldstrength was calculated and plotted as a function of the frequency ofcurrent (Hz) conducted through the electromagnetic edge dam 15, in whichthe distance at which the magnetic field strength was calculated rangedfrom 10 mm to 80 mm inward from the sidewall of steel casting rolls(reference line 1=10 mm, reference line 2=20 mm, reference line 3=30 m,reference line 4=40 mm, reference line 5=60 mm, and reference line 6=60mm). In each of the calculations, the height (H) of the magnetic polewas set at 8 mm, the distance (D) between the electromagnetic pole andthe roll face was set at 4 mm, and the roll gap (w) was set at 4 mm.Additionally, reference lines where plotted to indicate the minimum thefield strength required to contain a metal head having a height H₂ equalto 250 mm (reference line 7), 150 mm (reference line 8), 100 mm(reference line 9), and 50 mm (reference line 11). The plot depicted inFIG. 5 illustrates that the 0.079 T field density required for the 250mm metal head 8 could be created by this electromagnet in distances asfar as 20 mm into the roll gap.

The edge of the casting strip can therefore be contained inwards fromthe casting roll R₁, R₂ face (sidewall), if desired, by increasing thecurrent in the edge dam. It is noted that the field density decreasesrapidly at longer distances from the roll face and only small metal headheights, on the order of 50 mm, can be contained in distances 40 mm orgreater by the operation of this edge dam at 2000 amp turns. The rangeof containment can be extended further, if needed, by increasing themagnetomotive force (nI) on the edge dam. When increasing theelectromagnetic force, due consideration need to be given to the heatingeffect of the edge dam.

It is further noted that the plot depicted in FIG. 5 also illustratesthat the electromagnetic edge dam as utilized in the present inventionwould operate effectively at any chosen frequency. The loss in magneticfield becomes noticeable only for operation at frequencies greater than10 kHz.

In addition to the height of the molten metal head and the magneticfield density, the positioning of the electromagnetic edge dam withrespect to casting rollers may also be adjusted to provideelectromagnetic force lines to confine the molten metal M within themolding zone 20. Referring to FIG. 6, the electromagnetic edge dam 15may be positioned wherein the poles of the magnetic member are alignedto the sidewalls 13 of the casting rollers R₁, R₂. In one embodiment,the electromagnetic edge dam may be positioned wherein the poles of themagnetic member are distal from the sidewalls of each casting roller R₁,R₂. In the embodiments of the present invention in which a horizontalbelt casting apparatus is employed as depicted in FIG. 2 a, theelectromagnetic edge dam 15 may be positioned wherein each pole of themagnetic member is distal from to aligned to the adjacent sidewall ofthe casting belts B₁, B₂. For the purposes of this disclosure the term“distal from to aligned to the adjacent sidewall of the casting belts”is intended to denote that the poles of the electromagnetic edge dam donot extend towards the casting apparatuses centerline beyond a planedefined by the sidewall of the casting belts, but are positioned withinclose enough proximity to the sidewall of the castings belts to providea sufficient magnetic field to contain molten metal within the moldingzone.

The inventive electromagnetic edge dam will also perform in casters withrolls made from a non-magnetic (non-ferromagnetic) material, such ascopper. However, when the rollers comprise a non-magnetic material, thepenetration of the magnetic field into the roll gap may be limited andthus containment will typically occur on a plane close to the end of ofthe rolls. It may be possible to obtain penetration into the gap bycoating with a ferromagnetic material (such as iron, nickel or cobalt)the end faces and casting surfaces 200 of such rolls to the requireddepth of containment, as depicted in FIG. 8 d.

It is noted that prior casting apparatuses typically shape the magneticpoles of the electromagnetic devices and the casting rolls to focus themagnetic field towards the molding zone. In one example, prior castingrollers employ lips extending from the sidewall of each roller and mayhave further included magnetic poles having a geometry corresponding tothe extending lips of prior casting rollers. Contrary to prior castingapparatuses, the present invention does not require specially configuredcasting rollers to facilitate the focus of the magnetic field producedby the electromagnetic edge dam. In one embodiment of the presentinvention, the sidewalls 113 of the casting rollers R₁, R₂ may besubstantially planar. Further, the electromagnetic edge dam 15 of thepresent invention may be positioned so that the face of theelectromagnetic edge containment device is aligned to the face of thecasting roller's planar sidewall 113, wherein the electromagnetic edgedam 15 is in close proximity to the casting rollers R₁, R₂. Theelectromagnetic edge dam 15 may also be positioned distal from thecasting roller's sidewall 113. Regardless of the positioning of theelectromagnetic edge dam 15, the electromagnetic edge dam 15 ispositioned to provide sufficient electromagnetic force to contain themolten metal M within the molding zone 20.

The positioning of the edge dams 15 may be dependent on the current orfrequency utilized in the edge dam. For example, lower currents mayprovide lower magnitude electromagnetic force line and therefore be morelikely to require that the edge dam 15 be positioned in closer proximityto the molding zone 20. The higher the current conducted through theelectromagnetic edge dam the greater the magnitude of theelectromagnetic force lines and hence the father away theelectromagnetic edge dams may be positioned from the molding zone.

Referring to FIGS. 7 a-7 c, in one embodiment, the positioning of theelectromagnetic edge dam 15 and the magnitude of the electromagneticforce lines are selected to form a substantially flat sidewall (FIG. 7a), a convex sidewall (FIG. 7 b), or concave sidewall (FIG. 7 c) in themolten metal M within the molding zone 20. In one example, a current of2200 Amp/turns produces a casting strip having a concave sidewall; acurrent of 1200 Amp/turns produces a casting strip having asubstantially flat or straight sidewall; and a current of on the orderof 1200 Amp/turns produces casting strip having a substantially convexsidewall. It is noted that the above examples are provided forillustrative purposes only and are not intended to limit the presentinvention, as any current is applicable to the present invention, solong as the current provides sufficient containment forces to themolding zone 20 and does not result in excessive induction heating. Insome of the preferred embodiments of the present invention, in which thecasting strip's sidewall is concave or convex, the curvature of thesidewall may be defined by a radius that is approximately half themolten head height.

In another embodiment, the electromagnetic edge dam 15 may be configuredto provide molten metal within the molding zone having a convex sidewallrelative to the centerline of the molten metal M within the molding zone20. Preferably, the sidewall of the molten metal within the molding zoneis substantially aligned to the planar surface of the roller casters, asdepicted in FIGS. 8 a and 8 c. Alternatively, the electromagnetic edgedam 15 may be configured to project magnetic lines of force beyond thesidewall 113 of the casting rollers, wherein the molten metal isconfined interior to the edge of the roller casters, as depicted inFIGS. 8 b and 8 d.

The electromagnetic edge dam's 15 structure is illustrated in detail inFIG. 8 a, representing a sectional view of the edge dam apparatus 15illustrated in FIG. 2 a. In the preferred embodiment of the invention,the electromagnetic edge dam 15 is a magnet type of confinement systemand includes a generally C-shaped magnetic member. The magnetic member30 thus includes a core 32 having an upper arm or pole 34 and a lowerarm or pole 36 extending therefrom to define a generally C-shaped crosssection. The core 32, includes an induction coil winding 38 comprising acoil wound about the core 32 of the magnetic member 30 to establish aninduction coil. Thus, the winding is composed of a plurality ofconductors wound about the core 32 of the magnetic member 30. The corewindings 38 about the core 32 can be, made of solid metal such as copperwire.

Still referring to FIG. 8 a, the upper arm 34 terminates in a pole face42 where as the lower arm 36 terminates in a pole face 44, respectively,with the molten metal M being maintained therebetween. The pole faces 42and 44 thus define the surface from which the magnetic lines of forcegenerated by the magnetic element 30 with its induction coil 38 passfrom one of the pole faces 42 to the other pole face 44, as illustratedby the magnetic lines of force 48.

FIGS. 9 a-9 c illustrate different pole face 44 angles and orientationsin accordance with the present invention. It will be appreciated bythose skilled in the art that as the inter-pole-face gap 43 increases,the strength of the field across the gap decreases. FIG. 9 a illustratesa cross section of a magnetic member 30 wherein the pole faces 42 and 44have a negative angle relative to the vertical plane substantiallyperpendicular to the plane on which the casting is being drawn. Thenegative angle means that the inter-pole-face gap 43 is less at theoutside edge of each pole than at the inside edge of each pole face. Asa result, the containment forces created by the magnetic member shown inFIG. 9 c are stronger at the outside edge of each pole face than at theinside edge of each pole face. FIG. 9 b illustrates a cross section of amagnetic member 30 wherein the pole faces 42 and 44 have no anglerelative to the vertical plane substantially perpendicular to the planeon which the casting is being drawn. The zero angle means that theinter-pole-face gap 43 is the same at the inside edge of each pole faceand the outside edge of each pole face. As a result, the magnetic fieldcreated by the magnetic member shown in FIG. 9 b is relatively uniformacross each pole face. FIG. 9 c illustrates a cross section of amagnetic member 30 having pole faces 42 and 44 that are parallel in partand not parallel in part. The inside region of the pole faces 42 and 44have a negative angle relative to the horizontal.

In one embodiment of the present invention, the magnetic member 30 isformed from a ferromagnetic material such as silicon steel, and can beformed from a solid piece of such ferromagnetic material. Alternatively,the magnetic member 30 can be formed from multiple ferromagneticmaterials, such as the split core design depicted in Figure 10. Inanother embodiment, the magnetic member 30 can be formed from a seriesof laminated elements machined and secured together using mechanicalmeans, an adhesive or like means to yield the desired configuration, asdepicted in FIG. 1l. In many instances, the use of such laminates ispreferable, because laminates may serve to more uniformly distribute theflux lines in the magnetic member and reduce loss due to saturation ofthe magnetic member. In addition, for a magnetic member made oflaminated ferromagnetic material, the electrical energy dissipated asheat is also more evenly distributed and more easily removed,particularly where the adhesive employed to hold the laminate elementstogether has good thermal conductivity.

Referring back to FIGS. 8 a-8 d, surrounding the magnetic member 30 isan outer shield 50, which is preferably made of a material, and mostpreferably a metal, having structural rigidity and extremely highelectrical and thermal conductivities. Preferably, the outer shield 50is fabricated of copper, although other metals such as silver and goldcan likewise be used. The high electrical conductivity of the outershield 50 aids in containing the magnetic lines of force within themagnetic member while the good thermal conductivity aids in thedissipation of heat from the overall apparatus. As will be appreciatedby those skilled in the art, the outer shield 50 may be provided withcooling channels therein or brazed tubes thereon to distribute coolingfluid through or at the surface of the outer shield to further aid inthe removal of heat generated by the electromagnetic field. For example,an inlet can be employed to pass a cooling fluid through the outershield for removal from a discharge port when additional coolingcapability is required. Thus, the cooling fluid can be passed through aconduit within the outer shield to remove heat generated by theelectromagnetic field.

The electromagnetic edge dam employed in the practice of the presentinvention also includes an inner shield 56 dimensioned to fit within theC-shaped configuration of the magnetic member 30. The inner shield 56likewise serves to contain the magnetic lines of force generated by thecoil 38 of the magnetic member 30, insuring that the magnetic lines offorce are maintained within the magnetic member 30. In addition, it isalso possible, and some times desirable, to include within the innershield conduit means for the passage of a cooling fluid therethroughwhere it is desired to increase the ability to dissipate heat from themagnet. It is also possible to do away with the inner shield; especiallyso when using grain oriented silicon steel laminates where the fieldlines prefer to flow within the laminates.

The path of the magnetic field of the present invention is indicated inFIGS. 8 a thorough 8 d. In FIG. 8 a, magnetic field flows from one poleof the edge dam to the other in a plane essentially parallel to the sidefaces of the rolls. It is applicable to metallic rolls which arenon-ferromagnetic (such as copper). The field creates the containmentforces on the end faces of the rolls. FIG. 8 b illustrates the case whenthe field penetrates into the gap and contains the molten metal inwardsfrom the roll faces. This will be the case for ferromagnetic rolls andstrong fields. It can also be achieved by the application of aferromagnetic coating 200 of sufficient depth to the end faces and endof the casting surface of a non-ferromagnetic roll material, as depictedin FIG. 8 d.

In designing the electromagnetic containment apparatus employed in thepractice of this invention, a number of different techniques can be usedin dissipating heat generated by the electromagnetic field. As shown inFIG. 8 c, the windings 40 may be formed of an annular conductor having acentral opening 41 extending therethrough. Thus, cooled water can bepassed through the central opening of the windings 40 to aid in thedissipation of heat generated by the electromagnetic field. As shown inFIG. 12, the core 30 may also be equipped with a cooling conduit 47extending therethrough; in that way, a cooling fluid can be 370044-00038passed through the cooling conduit 47 to aid in the dissipation of heatgenerated by the electromagnetic field.

FIG. 12 illustrates one preferred embodiment of the present invention,wherein a mechanical edge dam 55 is used in conjunction with anelectromagnetic edge dam 15 having a magnetic member 30. The magneticmember 30 is preceded by the mechanical edge dam 55. The mechanical edgedam 55 shown should ideally have a ceramic-less surface and comprisemagnetic material to reduce the reluctance at the mouth of the moldingzone. A ceramic material may also be used to make mechanical edge dam 55if process conditions preclude the use of a metallic material. In oneembodiment of the present invention, the mechanical edge dam 55 ispositioned to ensure that the molten metal is contained within thecasting apparatus while being delivered from the tundish H to the feedtip T. Once the molten metal M reaches the feed tip T, containmentforces are provided by the electromagnetic edge dam 15. In thisarrangement, the service life of the mechanical edge dam 55 is increasedby the electromagnetic edge dam 15, since the electromagnetic edge dam15 is positioned in the most hostile portion of the casting apparatus.

The following examples are provided to further illustrate the presentinvention and demonstrate some advantages that arise therefrom. It isnot intended that the invention be limited to the specific examplesdisclosed.

EXAMPLE 1 Confirmation of Electromagnetic Push

Aluminum strip was cast in accordance with the present invention using acaster with steel rolls. The strip was then metallographically tested toconfirm the effect of the electromagnetic force on the molten metalwithin the molding zone. Test specimens were formed using a horizontalroller caster and a combination of electromagnetic and mechanical edgedams consistent with the present disclosure. Casting strips of threedifferent thicknesses (2.44 mm, 2.29 mm, and 2.16 mm) were then castoperating the electromagnetic edge dam at 2180 A turns. Samples werethen cut from the edges of the strips and were prepared formetallographic examination. It was observed that the center part of thecasting strip was pushed inwards as compared to the outer surfaces ofthe strip, as shown in FIGS. 14 a and 14 b. This observation confirmsthe confinement effect of the electromagnetic edge dam during casting,since the central portion of the strip is the last to solidify.

The depth of the confinement effect into the roll gap was estimated byfirst measuring the width of the casting strip at room temperature,wherein the width of the casting strip was approximately 400.5 mm. Fromthis measurement, the width of the strip within the molding zone can beestimated as 406 mm by adding the contraction that occurred duringsolidification and cooling to room temperature.

Taking into account that the width of the casting roll is approximately432 mm, it is evident that the magnetic field pushed the molten centerof the casting strip a distance of approximately 13 mm (13 mm=(432(widthof roller caster)−406)/2) from the casting roll face on each side of thecasting roll. More specifically, by subtracting the calculated width ofthe casting strip in the molding zone from the width of the castingroller the total displacement produced by the electromagnetic edge damsis calculated. The amount of displacement produced by a single edge damis calculated by the number of edge dams employed, which in thisexperiment consisted of two electromagnetic edge dams positioned atopposing ends of the casting rollers.

Similar electromagnetic push effects were observed for all threedifferent strip thickness (strip gauge), as summarized in the Tabledepicted in FIG. 13. The degree of magnetic push was measured as thedepth of the center portion of the strip with respect to the edges. Themagnetic push was somewhat higher for thinner gauge strip, since thenarrower roll gap would create a higher field density at any givendistance. It is believed that the difference in the magnetic pushbetween the two sides (drive side and operator side) of the casterrolls, as summarized in FIG. 13, is attributed to variations in thelocation of the electromagnets and the mechanical edge dams.

EXAMPLE 2 Control of Cast Strip Edge Profile

The edge profile of the as-cast strip was checked for operation atdifferent magnetomotive force levels in the electromagnet. The edgeprofile obtained at 2180 A turn operation shown in FIG. 14 wereconsidered unsuitable for subsequent rolling of the strip unless theedges were trimmed prior to rolling. In order to provide cast striphaving edge profiles suitable for rolling without additional machining,the magnetomotive force of the electromagnet was reduced to decrease thepush on the central portion of the casting strip so that the edgeprofile of the strip would be flat or slightly convex.

A flat edge profile was obtained in the casting strip at a current levelof 180 A (or 1620 A turns) being applied to the electromagnet. To obtaina flat edge profile, the magnetic field should be selected to justoffset the pressure produced by the molten metal in the molding zone,which is produced by the metal head with a minor contribution small rollpressure. Referring to FIG. 15, the edge of the casting strip made underthese conditions was flat and highly straight indicating that it couldbe rolled without trimming the edges of the casting strip or otheradditional machining.

This strip was rolled in-line successfully through four stands ofrolling mills. The casting strip was rolled from a 2.7 mm (0.107 inch)as-cast thickness to a thickness of approximately 0.36 mm (0.014 inch),which corresponded to an 87% reduction in thickness. Referring to FIG.16, the sheet made by this method showed only minor cracks at the edges,which could be removed by trimming prior to coiling.

Following proper adjustment of the electromagnetic edge dam, highquality edges are obtained in the as-cast strip which permits rolling tohigh reduction ratios saving materials and improving the efficiency ofthe process.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. An apparatus for strip casting of molten metal comprising: (a) a pairof casting rollers adapted to receive molten metal along a horizontalaxis, wherein a vertical distance separating the pair of casting rollersdefines a molding zone; (b) an electromagnetic edge containmentapparatus positioned on each side of the molding zone, comprising aninduction coil wound about a portion of a magnetic member to generatemagnetic lines of force upon application of a current, wherein saidmagnetic member comprises a first and second pole positioned distal fromand aligned with a sidewall of said pair of casting rollers and thecurrent provides magnetic lines of force perpendicular to saidhorizontal axis that contain the molten metal in contact with thecasting rollers with substantially no increase in temperature to themolten metal; and (c) a means for supplying the molten metal to themolding zone along said horizontal axis from a tundish, while ensuringsaid molten metal remains substantially non-oxidized, wherein thetundish is separated from the molding zone by a distance tosubstantially eliminate wave generation within the tundish by themagnetic lines of force.
 2. The apparatus of claim 1 wherein saidcurrent comprises an alternating current having a frequency ranging from40 Hz to 10,000 Hz.
 3. The apparatus of claim 1 wherein said currentcomprises less than 2,000 amp/turns.
 4. The apparatus of claim 1 whichincludes shield means positioned about the magnetic member.
 5. Theapparatus of claim 1, wherein the magnetic member has a generallyC-shaped configuration, including a core portion and parallel polesintegral with and extending therefrom.
 6. The apparatus of claim 5,wherein the induction coil is wound about the core of the magneticmember, in which the induction coil is coiled from 1 to 100 times aroundthe magnetic member.
 7. The apparatus of claim 1, wherein the verticaldistance separating the pair of casting rollers provides a metal headheight that allows for containment of the molten metal between thecasting rollers by the magnetic lines of force at said current without asubstantial increase in temperature of the molten metal resulting fromthe magnetic lines of force.
 8. The apparatus of claim 1, wherein thevertical distance separating the pair of casting rollers is less than1.0″.
 9. The apparatus of claim 1, wherein the magnetic member ispositioned to the molding zone to position the magnetic lines of forceto produce a convex sidewall, a concave sidewall, or a substantiallyflat sidewall to the molten metal within the molding zone.
 10. Theapparatus of claim 1, wherein the magnetic member is formed of aferromagnetic material from a stack of bonded or mechanically linkedlaminates or the magnetic member is formed from a solid core offerromagnetic material.
 11. The apparatus of claim 1, wherein said pairof casting rollers comprises a ferromagnetic material, non-ferromagneticmaterial, or a non-ferromagnetic material that is at least coated with aferromagnetic material on at least casting surfaces and said sidewallsof said pair of casting rollers.
 12. The apparatus of claim 1, whereinsaid sidewall of said pair of casting rollers is substantially planar.13. An apparatus for strip casting of molten metal comprising: (a) apair of opposing endless metal belts, each of the pair of opposingendless metal belts passing over a roller and having a peripherysubstantially aligned to a sidewall of the roller, said each of saidopposing endless metal belts having a surface for accepting moltenmetal, wherein a vertical dimension separation the pair of opposingendless metal belts defines a molding zone; (b) an electromagnetic edgecontainment apparatus positioned on each side of the molding zonecomprising an induction coil wound about a portion of a magnetic memberto generate magnetic lines of force upon application of a current,wherein the current provides magnetic lines of force that contain themolten metal within a width and in contact to at least a portion of saidpair of opposing endless metal belts with substantially no increase intemperature to the molten metal; and (c) a means for supplying saidmolten metal to the molding zone along a horizontal axis from a tundish,the tundish separated from said molding zone by a distance tosubstantially eliminate wave generation within the tundish by themagnetic lines of force.
 14. The apparatus of claim 13, wherein themagnetic member comprises an upper pole and a lower pole, the inductioncoil wound about a portion of the magnetic member to generate magneticlines of force passing from one of the upper and lower poles to theother, with the magnetic member being positioned such that the upper andlower poles direct magnetic lines of force establish containment forcesat the edges of the pair of opposing endless metal belts to contain themolten metal therebetween.
 15. The apparatus of claim 13, wherein thevertical distance separating the pair of opposing endless metal beltsprovides a metal head height that allows for containment of the moltenmetal between the pair of opposing endless metal belts by the magneticlines of force at said current without a substantially increase intemperature of the molten metal resulting from the magnetic lines offorce.
 16. The apparatus of claim 13, wherein the minimum verticaldistance separating the pair of opposing endless metal belts, at the nipof the caster, ranges from about 0.025″ to 0.25″.
 17. The apparatus ofclaim 13, wherein the magnetic member is positioned to the molding zoneto position the magnetic lines of force to produce a convex sidewall,concave sidewall or substantially flat sidewall to the molten metalwithin the molding zone.
 18. A cast metal strip comprising: a firstshell; a second shell; and a central portion between said first shelland said second shell, said central portion comprising grains having anequiaxed structure, wherein said cast metal strip has sidewall edgesbeing substantially uniform.
 19. The cast metal strip of claim 18wherein said first shell is an upper shell and said second shell is alower shell.
 20. The cast metal strip of claim 18, wherein said castmetal strip may be rolled without machining said sidewall edges.
 21. Thecast metal strip of claim 18 comprising aluminum and other light metalssuch as magnesium and zinc.
 22. The cast metal strip of claim 18,wherein said equiaxed structure is substantially globular.
 23. A castingapparatus comprising: (a) a pair of casting rollers adapted to receivemolten metal along a horizontal axis, wherein a vertical distanceseparating the pair of casting rollers defines a molding zone; (b) a tipdelivery structure positioned to supply the molten metal to the moldingzone along said horizontal axis from a tundish while ensuring saidmolten metal remains substantially non-oxidized; and (c) an edgecontainment apparatus positioned on each side of the molding zone, saidedge containment apparatus comprising: a mechanical edge dam positionedoverlying at least an end portion of said tip delivery structure andpartially extending towards said molding zone, and an electromagneticedge dam comprises a first and second magnetic pole positioned distalfrom and aligned to a sidewall of said pair of casting rollers andoverlying a portion of said mechanical edge dam partially extendingtowards said molding zone, wherein said electromagnetic edge damprovides magnetic lines of force perpendicular to said horizontal axisthat contain the molten metal in contact to the casting rollers.
 24. Thecasting apparatus of claim 23 wherein said tip delivery structure has alength that substantially eliminates wave generation within the tundishby the magnetic lines of force.
 25. The casting apparatus of claim 24wherein said electromagnetic edge dam comprises an induction coil woundabout a magnetic member to generate magnetic lines of force uponapplication of a current.
 26. The casting apparatus of claim 25 whereinsaid current provides magnetic lines of force that contain the moltenmetal in contact to the casting rollers with substantially no increasein temperature to the molten metal.
 27. A method of forming a cast metalstrip comprising providing molten metal to a molding zone along ahorizontal axis; containing said molten metal within said molding zonewith a magnetic containment means; and casting said molten metal into acast metal strip, wherein sidewall geometry of said cast metal strip isconfigured by adjusting said magnetic containment means.
 28. The methodof claim 27 wherein said sidewall geometry is flat or is concave orconvex relative to a centerline portion of said cast metal strip. 29.The method of claim 28 wherein said magnetic containment means comprisesan induction coil wound about a magnetic member to generate magneticlines of force upon application of a current, said magnetic memberhaving a first and second magnetic pole positioned distal from toadjacent to said molding zone.
 30. The method of claim 29 wherein saidadjusting said magnetic containment means comprises increasing ordecreasing said current through said induction coil.
 31. The method ofclaim 29 wherein said adjusting said magnetic containment meanscomprises moving said first and second magnetic poles adjacent to ordistal from said molding zone.